[ricardojoa]

Well, i got a question regarding difraction from cabinet edges.
If im not mistakne, the edges of the cabinets are usually rounded over to control difraction. My question is, wouldnt a beveled edges have better control since the egdes are straight?

[Letitroll98]

I wish I could explain the math or remember the link, but I can't right now, I'll perhaps look tomorrow.  But beveled is better than 90°, but not as good as radius.

[JLM]

The concept is to avoid any sharp edges.  In theory a sphere (like the Gallo balls) would be ideal (except for internal resonances).  A couple of egg shaped speakers have been developed for 2-way designs, but are expensive to set up for manufacturing.

[jtwrace]

[mcgsxr]

Not being a science guy, I will leave the detailed explanations to those who are.

I think the basic concept is that any sharp edge concentrates the diffusion at a given frequency.  Rounding over spreads the frequencies accentuated by the edge of the baffle.

Same idea as offsetting an OB driver in the baffle.

[ricardojoa]

If the cabinet is slimmer, the round or beveled edge have less effect on diffraction, is that right?
I also noticed, for example a speaker with 5 inch driver , the overall driver will usually sit on the baffle that is under the interior width of the cabinet. What happens if the frame of the driver actually sit over slightlly over the interior width of the cabinet? That way a slimmer cabinet can be built, but i dont see people doing it, what kind of compromise can that have?

[TRADERXFAN]

The concept is to avoid any sharp edges.  In theory a sphere (like the Gallo balls) would be ideal (except for internal resonances).  A couple of egg shaped speakers have been developed for 2-way designs, but are expensive to set up for manufacturing.

edit- Nevermind, I was going to say someething that was incorrect. Thinking of cylinder instead of sphere.

[Letitroll98]

Here's a nice picture for those of us who like cartoons better than the science channel:



And here's the link for modeling enclosure shapes that I was thinking of:

http://www.pvconsultants.com/audio/diffraction/downloadbds.htm

Note these are both available by mining the Speaker Design Links thread at the top of this circle's page.  Thank you very much.

[Big Red Machine]

Everything is a compromise in speaker design.  A narrower cabinet is nice, hence something like a SS10/12.  But these designs are more expensive than a standard rectangular box which has the required internal volume and allows someone to reach inside and mount the guts.  As far as rounded versus square, not sure you could hear that small of an impact with a reasonably narrow cabinet to start with.  As far as offsetting a tweeter, this keeps the driver from replicating the bounced frequencies on both sides of the driver and making it twice as bad.  Offsetting the driver produces three sets of bounces that hopefully do not coincide (left, right, top).  So whatever beams back at you is not overemphasized. 

If the cabinet is slimmer, the round or beveled edge have less effect on diffraction, is that right?
I also noticed, for example a speaker with 5 inch driver , the overall driver will usually sit on the baffle that is under the interior width of the cabinet. What happens if the frame of the driver actually sit over slightlly over the interior width of the cabinet? That way a slimmer cabinet can be built, but i dont see people doing it, what kind of compromise can that have?

[*Scotty*]

Felt, and lots of it, helps enormously with diffraction problems. As you can see from Letitroll98's graphic, diffraction occurs anytime a wavefront hits a sharp edge.
A narrow baffle does not solve the problem it only moves the generation of a secondary source of radiation closer in time to the primary source. The smearing is reduced but is not eliminated.
 Basically, any loudspeaker you see has the problem and it is virtually inescapable. Felt is also kind of ugly which is why almost no manufacturer will cover up their pretty cabinet work. The WAF goes into the toilet and sales resistance goes up. A bad case of diffraction from the baffle area around the tweeter and the edge of the baffle creates a complex interference pattern which causes the HF response to be ragged and not smooth and flat as it should be.
 See the links below starting with LINKWITZ LAB for detailed explanations and a very good explanation including graphics showing the effects of destructive interference on the HF response curve.
http://www.linkwitzlab.com/diffraction.htm
http://www.linkwitzlab.com/faq.htm#Q8
http://www.speakerdesign.net/understand.html
Scotty

[redbook]

  I run a pair of JBL Ti 120s with the usual 90degree edges. I have had a noticable smoother sound by applying the little square felt sticky pads on either side of both the tweeter and mid driver. They look neat and some friends have thought they were originally there.   

[Quiet Earth]

The biggest problem I see with chasing diffraction is that you end up eliminating the baffle which is a worse problem than having a little diffraction with the appropriate baffle.

Kinda like chasing jitter . . . where you mangle the signal into something that it never was in the first place, so you are left with a poor facsimile of the music with no jitter.

[Letitroll98]

I agree to a point.  Most of the proffesional applications that I've seen leave portions of the baffle intact, applying felt judiciously and one assumes with knowledge of the issues you mentioned.  So experimenting might be better than mass application.

[bummrush]

This won't help anybody but here I go from what I gather from this is you can 10 different people and get no answers that help. I've heard round are better ,,, square corners better . Does anybody REALLY think there are definitive answers on this.

[S Clark]

This won't help anybody but here I go from what I gather from this is you can 10 different people and get no answers that help. I've heard round are better ,,, square corners better . Does anybody REALLY think there are definitive answers on this.

Yes there are definitive answers, and square is not as good as rounded.  Dennis Murphy measured two identical speakers with the only difference being the round over.  See http://murphyblaster.com/content.php?f=cabinets.html
Also, member jimgoulding sells a felt product custom fitted to your speaker for taming edge diffraction- at very reasonable cost. I've also seen the effects on my own measuring system. 

[TRADERXFAN]

Yes there is definitive answers. Diffraction is a scientific fact, and letitroll even gave a simulation.

So not sure what you mean by "no answers that help"...  Some have shown you about rounded over corners, soft edge transitions, etc. Others use felt, etc. There are options to deal with it in the design stage.

--There are always going to be varying degrees of perception and preference, as with anything in this hobby, so I hope that isn't what is putting you off.

[richidoo]

The radius of the roundover, or the size of the edge chamfer is proportional to the largest wavelength of diffraction. A 1" roundover adds some HF refinement, but is not big enough not to get into the heart of the midrange where diffraction removal gives an obvious benefit. I've heard several spheres and they all have a special something, very clear, easy, uncongested, relaxed and open.

planet10 has posted a great picture of various shape box bevels and their effect on diffraction. A 6" bevel is almost as good as a sphere.
http://www.audiocircle.com/index.php?topic=98591.0

[dflee]

Is defraction more noticeable in near field or the same for far? From the pictures I've seen it seems like the sound from edges doesn't seem to travel very much distance (or is this just my non knowledgeable way of looking at it).

[J Fallows]

 
Here's an explanation of diffraction from another speaker scientist and a great guy:
http://www.salksound.com/wp/
Scroll down to the second topic.
Don't think the original question of rounded or beveled is covered though.

[TRADERXFAN]

Is defraction more noticeable in near field or the same for far? From the pictures I've seen it seems like the sound from edges doesn't seem to travel very much distance (or is this just my non knowledgeable way of looking at it).

The diffraction "sounds" to you like another reproduction of the original sound, slightly delayed, for the affected frequency.